The present invention relates to photonic devices.
Silicon is the material of choice for the vast majority of microelectronic applications. Silicon is inexpensive and silicon-based processing techniques are well established. However, silicon possesses an indirect band gap and so some optical processes, such as photon emission, require the assistance of a phonon of a suitable wavevector, thus severely limiting efficiency of these processes. As a result, the use of silicon in some photonic applications, such as the manufacture of light emitting diodes, semiconductor lasers and optical modulators, is severely limited.
Phonon induced luminescence in compound semiconductors is disclosed by K. F. Renk in xe2x80x9cNon-equilibrium Phonons in Non-metallic Crystalsxe2x80x9d, Eisenmenger and Kaplyanskii Eds., North-Holland, 1986). These compound semiconductors, however, exhibit lattice polarisation and strong lattice coupling and are already efficient photon generators.
Attempts to make silicon an efficient photon generator are disclosed in xe2x80x9cSilicon Based Optoelectronic Materialsxe2x80x9d, Tischler et al. Eds., Material Research Society Proc., 298 (1993). The methods disclosed make use of quantum confinement and Si:SiGe heterostructures. However, these methods have not been particularly successful and devices based on these methods certainly do not lend themselves to conventional silicon-based processing techniques.
With a view to overcoming this difficulty, the present invention provides a photon emission device comprising a region of relatively low-efficiency photon emission material and a phonon generator operable to supply phonons to said region of relatively low-efficiency photon emission material so as to make it emit photons with a relatively high efficiency.
Said phonon generator may comprise an input structure to receive electromagnetic energy so as to produce phonons. Said phonon generator may comprise a converter to convert electrical excitations into lattice excitations. Said phonon generator may comprise an electrode to apply an electric field so as to produce phonons.
Said photon generator may comprise a fabricated device arranged on a substrate.
Said region of relatively low-efficiency photon emission material may comprise indirect band gap semiconductor material, such as silicon.
Said phonon generator may comprise a local lattice polarizer, such as a doped, compensated semiconductor, or a first layer of semiconductor doped with n-type impurities and a second layer of semiconductor doped with p-type semiconductor. Said first layer and said second layer may be separated by 1-5 nm.
Said phonon generator further may include an electric field generator to stimulate phonon generation. Said electric field may be provided by an electrode disposed at an interface with said local lattice polarizer.
Said electric field generator may comprise an electrode and an insulator, wherein said insulator may be disposed between said local lattice polarizer and said electrode.
Said phonon generator may further comprise an electron-hole pair generator, for example in response to a pulse of electromagnetic radiation. Said pulse of electromagnetic radiation may be of duration less than 100 fs. Said electromagnetic radiation may have an energy above the value of band gap of said doped, compensated semiconductor material.
Said electron-hole pair generator may comprise an electric pulse and said pulse may have duration less than 50 ps and a pulse height of the order of a few volts.
Said phonon generator may comprise a hot-electron injector. Said hot-electron injector may comprise an electrode and a layer of insulator.
Said device may further comprise a hot-electron thermalizer so as to create phonons.
Said electrode may comprise a metal, which may be aluminium.
Said insulator may comprise silicon dioxide or silicon nitride and may have a thickness less than 20 nm.
An advantage of the invention is that it allows the integration of photonic technology with conventional silicon-based logic circuitry and memory. This is particularly beneficial to applications in telecommunications and computing.
According to the present invention there is also provided a method of operating a phonon emission device comprising a region of relatively low-efficiency photon emission material said method comprising supplying phonons to said region of relatively low-efficiency photon emission material so as to make it emit phonons with a relatively high-efficiency.
According to the present invention there is still further provided a modulator comprising a region of optically transparent material and a phonon generator operable to supply phonons to said region of optically transparent material so as to increase photon absorption therein.